Provided is a semiconductor device including a fin-type field effect transistor (FinFET). The first FinFET includes a first gate structure and the first gate structure includes a first work function layer. The first work function layer includes a first layer and a second layer. The first layer is disposed over the second layer. The second layer includes a base material and a dopant doped in the base material. The dopant comprises Al, Ta, W, or a combination thereof. The first layer and the second layer comprise different materials. A method of manufacturing the semiconductor device is also provided.